Tubular prostheses, such as stents, grafts, and stent-grafts are known for treating abnormalities in various passageways of the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts of a biocompatible graft material supported by a framework, for e.g., one or more stent or stent-like structures, to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier. When implanting a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximal to or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distal to or downstream of the diseased portion of the vessel. In this manner, the stent-graft extends through and spans the aneurysmal sac and extends beyond the proximal and distal ends thereof to replace or bypass the dilated wall.
Such tubular prostheses are known to be implanted in either an open surgical procedure or by a minimally invasive endovascular/endoluminal approach. Minimally invasive endovascular stent-grafts for use in treating aneurysms are often preferred over traditional open surgery techniques where the diseased vessel is surgically opened, and a graft is sutured into position bypassing the aneurysm. The endovascular approach generally involves opening a vein or artery with a needle, inserting a guidewire into the vein or artery through the lumen of the needle, withdrawing the needle, inserting over the guidewire a dilator located inside an associated sheath introducer having a hemostasis valve, removing the dilator and inserting a delivery catheter through the hemostasis valve and sheath introducer into the blood vessel. The delivery catheter with the stent-graft secured therein may then be routed through the vasculature to the target site. For example, a stent-graft delivery catheter loaded with a stent-graft can be percutaneously introduced into the vasculature, for e.g., into a femoral artery, and the stent-graft delivered endovascularly across an aneurysm where it is then deployed.
Specialized endovascular stent-grafts have been developed for the treatment of thoracic aortic aneurysms. A thoracic aortic aneurysm a bulge that forms in the wall of the aorta in the area of the aortic arch or just below the aortic arch. Emanating from the aortic arch are three branch arteries, the innominate or brachiocephalic artery, the left common carotid artery, and the left subclavian artery. In some cases, an aneurysm in the aortic arch may extend into one of the branch arteries, or the aneurysm is located in the arch such that a main stent graft used to bypass the aneurysm will block access to the one or more of the branch arteries. Accordingly, a branch stent graft may extend through a fenestration in the main stent graft and extend into the branch artery.
However, the aortic arch represents a challenging design environment due to a significant amount of cardiac and reparatory movement. Such movement requires a branch stent graft with significant flexibility and durability to withstand such movement over and extended period of time. Further, in some cases, the fenestration of the main stent graft is not aligned with the branch artery. In such cases, the branch stent graft extends from the fenestration in the main stent graft, extends within the aorta for a short distance, and then extends into the branch artery (offset configuration). In such situations, significant flexibility is required and sufficient radial force to maintain the branch stent graft open against the force of the main stent graft while in the aorta.
Currently there are no commercially available branch stent grafts specifically designed for the aortic arch. Branch stent grafts used for other areas are not suitable for use in the aortic arch branch arteries. Known self expanding stent grafts lack the radial force required to perfuse the side branch, especially if the fenestrated aortic stent graft is deployed in an offset configuration. Known balloon expandable stent grafts are generally too stiff to decouple the large amount of motion occurring in the arch from the perfused branch vessel and these rigid stents may fracture. Accordingly, there is a need for a branch stent graft with sufficient flexibility and durability to withstand forces in the aortic arch.
With some balloon expandable stents or stent grafts, there can be a problem with foreshortening of the stent or stent graft when it is expanded by the balloon. Foreshortening results in a stent or stent graft that, when expanded to its radially expanded configuration, is shorter than expected or desired. In such a situation, the stent or stent graft does not cover the desired length of a treatment site, resulting in an untreated area or requiring delivery of an additional stent or stent graft to cover the untreated area. Foreshortening may occur due to the design of the stent and the fact that the balloon is generally slightly longer than the stent or stent graft disposed thereon. Because the stent or stent graft resists expansion of the balloon where the stent or stent graft is mounted on the balloon, the proximal and distal ends of the balloon tend to first. This pushes the proximal and distal ends of the stent or stent graft towards each other, thereby causing foreshortening. Accordingly, there is a need for a balloon catheter with an apparatus to reduce or eliminate foreshortening when radially expanding in a stent or stent graft mounted thereon.